Dating origins polyploidy events
Because of its economic importance and tremendous genetic and genomic resources available, rice along with its wild relatives has become a unique model for both theoretical studies and practical crop improvement. punctata) was found, which is widely distributed from east to west Africa (Fig. In addition, the origin time of BBCC tetraploids in Oryza has been largely unknown with only O. Here, we sampled multiple populations from all the species involving the B-, C- and BC-genome types.Particularly, with the completion of genome sequencing of two rice subspecies, the initiation and implementation of the Oryza Map Alignment Project (OMAP) have laid an important foundation for a complete genomic interrogation of the wild relatives of rice. Based on sequences of biparentally inherited nuclear genes and maternally inherited chloroplast regions, in conjunction with phylogenetic analyses and relaxed molecular dating, we fully resolved the phylogenetic relationships of these species, and particularly, determined the parental donors of all the BC-genome tetraploid species with their divergence times estimated.Hexaploidies can form in either one step (instant triplication of the genome) or two steps ( 1) tetraploidy, 2) a tetraploid gamete fuses with a diploid gamete creating a sterile triploid which then regains fertility by doubling its genome again, creating a hexaploid). Bread wheat is an excellent example of this process where most of the intermediate species still exist.Einkorn wheat is a diploid containing only the A genome.
Previous studies showed that many valuable genes or alleles had been successfully transferred to cultivated rice from tetraploids, such as O. grandiglumis (CCDD), and have significantly increased rice yield and resistance to various diseases and pests. By illustrating the origin pattern of the BC-genome tetraploids in the rice genus, these investigations not only improve our understanding of evolutionary patterns of allopolyploid formation in the model system but also lay important foundation for utilization the wild rice germplasm in rice breeding and genetic improvement. eichingeri in the germplasm bank but confirmed to be tetraploid O. One accession of Oryza granulata with the G genome was used as an outgroup.
Polyploidy has long been considered a major force in plant evolution. Ledyard Stebbins, Jr., an architect of the Modern Synthesis, elegantly addressed a broad range of topics, from genes to chromosomes to deep phylogeny, but some of his most lasting insights came in the study of polyploidy.
Here, we review the immense impact of his work on polyploidy over more than 60 years, from his entrance into this fledgling field in the 1920s until the end of his career.
Polyploidy, or whole genome duplication (WGD), is now recognized as a major evolutionary force not only in plants, but also in all eukaryotes (e.g., Mable, 2003; Gregory and Mable, 2005).
WGD generally results in instant speciation, increasing biodiversity and providing new genetic material for evolution (e.g., Levin, 1983, 2002).Identifying and characterizing plant paleopolyploidies is ongoing research.